The investigation of signed languages is crucial to our understanding of the neurobiology of human language, as well as to our understanding of deafness and the design of policies and programs for deaf individuals. We have developed an integrated approach for studying the effects of the visual-gestural modality on on-line language production, on the interface between language and cognition, and on the neural systems that underlie language. A coherent set of experiments addresses each of these issues. Section I: Effects of modality on language production. Currently, very little is known about the psycholinguistic mechanisms that translate thoughts into linguistic expression for signers, and it is unclear whether models of speech production can simply be appropriated for sign language. We will utilize various psycholinguistic techniques and data to develop a model of sign production (e.g., "tip of the fingers" effects; "slips of the hand," and monitoring paradigms). Our aim is to account for unique aspects of the visual manual modality that lead to disparities between sign and speech production. Section II: The interplay between visual-gestural language and visual-motor cognitive systems. The distinct biological basis of sign language results in a unique interface between vision and language and between action systems and language production. One aim is to identify structural parallels between the visual parsing of motion and the linguistic expression of motion events. Another set of studies examines interactions between perception and action, exploring a possible "motor theory of sign perception" account of sign language processing and the effects of linguistic knowledge on visual cognition (e.g., representational momentum). In essence, we use sign language as a tool to investigate the nature of cognitive modularity and interactivity. Section III: The functional neural organization for language. Paralleling Sections I and II, we use functional Magnetic Resonance Imaging (fMRI) to investigate a) the neural systems underlying sign production, b) the possibility of a "mirror system" for sign perception, and c) the neural basis for the structural similarity between vision and sign language perception, specifically with respect to motion processing. In addition, we continue our investigation of the neural substrates underlying the perception of linguistic and emotional facial expressions in deaf signers, focusing on the linguistic modulation of neural regions devoted to face processing.